The Evolution of the Sciences 



could have rallied physicists, at first sceptical, 

 round the theoretical views of the English school. 

 They all agree to-day in admitting that the 

 kathode stream consists of material particles, 

 each with a mass equal to one thousandth of the 

 mass of an atom of hydrogen. We have here a 

 new material element, which has been called an 

 electron or corpuscle, and this electron is invari- 

 ably found to have the same mass, whatever gas 

 may have been left in the Rontgen tube; it 

 further appears unaltered in all the phenomena 

 to be described later on: emission from radio- 

 active bodies, from flames, from sparks, from 

 metals exposed to light; its speed alone varies; 

 it seems therefore to constitute the primordial 

 unit of disaggregated matter. 



This shows all the fragility of our theories. 

 Scientistshad required centuries to find the atoms, 

 last and indivisible elements of matter; they 

 had succeeded in counting and weighing them, 

 in discovering that each cubic millimetre of the 

 air surrounding us contains ten thousand billions 

 of them, moving in all directions with speeds of 

 nearly 500 yards per second. Suddenly the 



spectacle changes, the atom falls to dust, and the 



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